The present invention relates to electric current sources based on fuel elements.
Hydrogen is a “clean fuel” because it can be reacted with oxygen in hydrogen-consuming devices, such as a fuel cell or combustion engine, to produce energy and water. Virtually no other reaction byproducts are produced in the exhaust. As a result, the use of hydrogen as a fuel effectively solves many environmental problems associated with the use of petroleum based fuels. Safe and efficient storage of hydrogen gas is, therefore, essential for many applications that can use hydrogen. In particular, minimizing volume, weight and complexity of the hydrogen storage systems are important factors in mobile applications.
The development of fuel cells as replacements for batteries in portable electronic devices, including many popular consumer electronics such as personal data assistants, cellular phones and laptop computers is dependent on finding a convenient and safe hydrogen source. The technology to create small-scale systems for hydrogen supply, storage and delivery has not yet matched the advancements in miniaturization achieved with fuel cells.
A hydrogen fuel cell for portable applications needs to be compact and lightweight, have a high gravimetric hydrogen storage density, and be operable in any orientation. Additionally, it should be easy to match the control of the system's hydrogen flow rate and pressure to the operating demands of the fuel cell.
The existing hydrogen storage options, which include compressed and liquid hydrogen, hydrided metal alloys, and carbon nanotubes, have characteristics which complicate their use in small consumer applications. For instance, compressed hydrogen and liquid hydrogen require heavy tanks and regulators for storage and delivery, metal hydrides require added heat to release their stored hydrogen, and carbon nanotubes must be kept pressurized.
Alternatives for hydrogen storage and generation include the class of compounds known as chemical hydrides, such as the alkali metal hydrides, the alkali metal aluminum hydrides and the alkali metal borohydride. The hydrolysis reactions of many complex metal hydrides, including sodium borohydride, (NaBH4) have been commonly used for the generation of hydrogen gas.
In those applications where a steady and constant supply of hydrogen is required, it is possible to construct hydrogen generation apparatus that control the contact of a catalyst with the hydride fuel. Such generators typically use a two-tank system, one for fuel and the other for discharged product. The hydrogen generation reaction occurs in a third chamber that contains a metal catalyst and connects the two tanks. However, such two-tank designs are not typically directionally independent or amenable to miniaturization.